Fix MD5 calculations in Digest auth to HTTP proxies

* Remove a trailing space after the literal "CONNECT" method
  string. This string is passed in to
  QAuthenticatorPrivate::calculateResponse, which computes an MD5 hash
  on the string if a proxy is using certain flavors of Digest
  authentication.

  See https://bugreports.qt-project.org/browse/QTBUG-32182